<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<div id='l1' style="font-size: 30px;background-color: green">123</div>
<script type="text/javascript">
    var i= document.getElementById("l1");
    i.style.backgroundColor="pink";
</script>
</body>
</html>